Method of making photocells



Oct. 8, 1957 METHOD OF MAKING PHOTOCELLS Filed June 18, 1953 ATTORNEYUnited States Patent Ofifice 2,809,115 a Patented Oct. 3, 1957 METHOD OFMAKING PHOTOCELLS Oran T. Mcllvaine, St. Charles, Iii.

Application June 18, 1953, Serial No. 362,450

4 Claims. (Cl. 117--215) This application is a continuation-in-part ofmy prior application for Photocells, Serial No. 275,435, filed March 7,1952,11ow Patent No. 2,654,819, granted October 6, 1953.

This invention relates to improvements in photocells and moreparticularly to photo-sensitive or photo-conductive cells.

In making such cells heretofore it has been necessary to paint or drawon a base surface lines of silver, platinum, or other metal, beforeactivation by lead sulfide or other semiconductors. Such operations inpreparing the cells are slow and tedious, and require relatively largeareas for producing the elements of the cell.

An object of this invention is to improve the process of makingphotocells of this character, to expedite the manufacture thereof, andto produce cells of relatively minute size.

A further object of the invention is to provide photoconductive cells ofthe minute size which can be used in many installations where such cellshave not been available for use heretofore.

These objects can be accomplished by applying the lines of conductingmaterial onto a base surface, such as a flat surface, in close relationto each other. These lines may be applied chemically which enables thelines to be in close side-by-side relation, and to be relatively finelines, much more compactly arranged than would be possible where theyare painted or drawn by hand. Then, after sensitizing the lines byevaporating the semiconductive metal, such as lead sulfide, germanium orthe like thereon, the base surface can be cut to form a multiplicity ofminute photocells.

The semiconductor coating can be covered, if desired, with a transparentor other covering material such as varnish, plastic, etc., to protectthe same during the treating operation and preparation of the individualcells.

The invention is illustrated in the accompanying drawings in which:

Fig. 1 shows the base material having lines applied thereto;

Fig. 2 shows diagrammatically the activation and protection of the base;

Fig. 3 shows the step of cutting out the individual cells by a stampingor punching operation;

Fig. 4 is a plan view of a completed cell thus formed; and

Fig. 5 is a perspective view of a treating tray or vat.

Referring to Fig. l, I have shown a base surface which can be eitherfiat or curved, as desired, and may be made of any suitable insulatingmaterial, preferably a thin sheet 1. It is possible to use glass, mica,or other substances suitable for the purpose, which should have asurface capable of receiving the lines to be applied thereto in closerelation, but may be either smooth or ground.

A series of lines, generally designated at 2, are applied to the surface1 of a suitable conducting material, such as silver, platinum, tungsten,graphite, or the like.

After thus forming the lines on the base 1 by ruling or otherwise, asemiconductor may be deposited thereover. Any of the known or usualmaterials for this purpose may be employed, such as lead sulfide,thorium, silicon, germanium, etc. Such a semiconductor can be depositedchemically, as by placing the sheet 1 or formed element in a tray or vatT in which it is subjected to a chemical treatment. If the treatment isto be applied in a tray, as indicated generally at T in Fig. 5, thesolution is first put in the tray and then the sheet 1 to be covered issuspended in the solution, so that just the bottom side of the sheet isin Contact with the solution. This will give a coating free from anysediment or any particles that will settle out. if coated in a tank, twosheets can be coated at one time by placing them back-to-back andsuspending them on the edge in the tank. This would also prevent anysediment from collecting on the plates.

The solution for lead sulfide can be made in the following manner: Alead salt, such as lead acetate, is mixed with distilled water to give adilute solution. Then a soluble salt, containing sulfur and oxygen, suchas potassium thiosulphate or other similar salt, is mixed to give adilute solution. These two solutions are then mixed in proportions ofone part of the latter to four parts of the former solution. After thusmixing the solutions, they are placed in a tray to which one part ofpotassium hydroxide is added, being stirred in, and the plate or platesto be coated is then placed in the tray at once in the manner described.These proportions may be changed somewhat to vary the results obtained,as desired.

As an example, 5 cc. of a lead salt may be mixed with 20 cc. ofthiosulphide, to which is added 5 cc. of potassium hydroxide. This willbe enough solution to cover from four tosix square inches.

The deposit will start to form at once and will continue for an hour ormore, depending upon the variation of the parts added. The rate ofdeposit will determine the type of coating formed. Any type of coating,from a mirror-like surface to a dull gray or granular deposit can beformed by changing the concentrations somewhat. This in turn controlsthe light response given by the coating. By adding trace elements to thesolution during the deposition, a substantial control can be had of thephotoelectric response.

This photo-electric response can be controlled also to a substantialextent by heat treating the coating after forming and drying. As anexample, baking in an oxygen atmosphere will give sensitivity, and othermethods well known in the art can also be used for varying effects.

In some cases, after the plate has been coated chemically, it may bedried and placed in a vacuum chamber for further processing. Here it canbe treated with oxygen under elevated temperatures and reduced pressures to procure the desired photo response. An example thereof isillustrated in Fig. 2, in which the vacuum chamber is designated at 3and the source of oxygen may be admitted thereto, as indicated at 4.

Thereafter it is preferred to coat the surface with a suitableprotective material such as transparent, translucent or opaqueinsulating material, such as varnish, resin or plastic, which may beapplied by dipping or otherwise. This coating material will cover thesurface of the semiconductor material on the base 1 and protect thelatter in the subsequent operations without interfering with itseffectiveness in use.

Thereafter, the chamber 3 is opened and the base 5., if made in multiplesize, is cut up into individual cell elements. This may be accomplishedby an assembly of punch or die elements, generally indicated at 5 inFig. 3, which will sever the base 1 into a multiplicity of minuteelements. The punch or die elements 5 should be so disposed as to crossa pair of adjacent metal conductor lines, as indicated in Fig. 3,preferably slitting the base midway between a pair of said lines 2. Thisproduces 21 segment of the base, having a pair of conductor lines 2extending across the same, as indicated at 2 in Pig. 4, where theindividual cell element is designated generally at 6, which results fromthe stamping out of the treated base in the manner described. Thisstamping process preferably cuts the base into equal sized cells, amultiplicity of which may be formed from a single sheet, in the mannerdescribed, although these may be either square, rectangular, or of anyother shape.

A portion of the covering material, such as plastic or varnish, may bestripped off at the ends of the conductor lines 2 to provide forelectrical connections therewith, or the entire covering material may beremoved, especially if the cell is to be used in vacuum.

The semiconductors described above may be used either single or combinedin proper proportions to produce the spectral response desired. They maybe mixed together in the solution, as will be evident to any onefamiliar with the art.

The process may be carried out with a thin sheet of mica, glass, or thelike. if the sheet is formed of mica, it can be cut with dies, asdescribed above; or if formed of glass, the back of the sheet can beruled with a diamond cutter so that each individual cell can be brokenoff readily.

The cells can also be prepared in units before having the cutter appliedthereto, and these individual units can be attached to a large sheet forprocessing in the manner described by depositing the semiconductorcoating thereon and preferably also a protective coating thereover ofplastic or other suitable material. The latter can be applied to thesheet or to the individual elements and may be transparent, translucent,or opaque. The coating material will protect the sensitized elementsfrom moisture, handling and other outside influences which might affectthe operation thereof.

It is possible to produce in this way very simply and inexpensively amultiplicity of minute photocells without the slow and laborious methodof drawing or painting the conductor lines on the base surface and, atthe same time, cells of very much smaller size can be used due to thesmall area required where the lines are applied in the manner described,especially by printing or photo-engraving the lines on the base surface.

While the invention has been illustrated and described in certainembodiments, it is recognized that variations and changes may be madetherein without departing from the invention as defined in the claims.

I claim:

1. A method of making a photocell comprising applying a plurality oflines of conducting material onto an insulating base surface, andapplying a solution of a semiconductor thereover to sensitize saidsurface, said solution being formed by mixing a solution of a lead saltin water with a. second solution of a soluble salt containing sulfur andoxygen.

2. A method of making a photocell comprising applying a plurality oflines of conducting material onto an insulating base surface, applying asolution of a semiconductor thereover to sensitize said surface, saidsolution being formed by mixing a solution of a lead salt in water witha second solution of a soluble salt containing sulfur and oxygen, anddipping the coatc surface of the base in said solution.

3. A method of making a photocell comprising applying a plurality oflines of conducting material onto insulating base surface, applying asolution of a semiconductor thereover to sensitize said surface, saidsolution being formed by mixing a solution of a lead salt in water witha second solution of a soluble salt containing surfur and oxygen, andthereafter coating the base surface with a protective film.

4. A method of making a photocell comprising applying a plurality oflines of conducting material onto a insulating base surface, andapplying a solution of a semiconductor thereover to sensitize saidsurface, said solution being formed by mixing a solution of asemiconductor selected from the class consisting of lead sulfide andgermanium, with a second solution of a soluble salt containing sulfurand oxygen.

References Cited in the file of this patent UN TED STAT S PATENTS919,078 Ribbe Apr. 20, i969 2,629,166 Marsten et al. Feb. 24, 19532,654,819 Mcllvaine Oct. 6, 1953 FOREIGN PATENTS 610,361 Great BritainOct. 14, 1.948

1. A METHOF OF MAKING A PHOTOCELL COMPRISING APPLYING A PLURALITY OFLINES OF CONDUCTING MATERIAL ONTO AN INSULATING BASE SURFACE, ANDAPPLYING A SOLUTION OF A SEMICONDUCTOR THEREOVER TO SENITIZE SAIDSURFACE, SAID SOLUTION BEING FORMED BY MIXING A SOLUTION OF A LEAD SALTIN WATER WITH A SECOND SOLUTION OF A SOLUBLE SALT CONTAINING SULFUR ANDOXYGEN.